Casing heater



July 9, 1963 L. c. CRONBERGER 3,097,232

CASING HEATER Filed Sept. 13, 1960 I N VEN TOR. Lu/Aer C. Croneryer United States Patent M 3,097,282 CASING HEATER Luther C. Cronberger, Tulsa, Okla assignor to The Dow Chemical Company, Midland, Micl1., a corporation of Delaware Filed Sept. 13, 1960, Ser. No. 55,802 7 Claims. (Cl. 219-1049) This invention relates to oil and gas well heaters and particularly to induction type heaters which are adapted for down-hole usage.

Down-hole heating tools find usage in several operations in well service. For example, heating well casing to accelerate the setting time of cement lying between the casing and the annulus of the Well bore and heating the tubing in a well to prevent the deposition of parafii-n or other materials contained in formation fluids are uses of such devices.

Down-hole heating tools are either of a combustion type or are electrically energized. So called induction heating units are known for such service in wells, but have not proven as satisfactory as has been desired from the standpoint of cost, eflieiency of operation, or freedom from operational difiiculties or maintenance.

Accordingly, a principal object of this invention is to provide an improved down hole heating tool which is especially adapted for use as a casing heater.

Another object of this invention is to provide an improved, economical and efiicient down-hole heating tool.

In accordance with this invention there is provided a down-hole casing heater comprising, disposed about an axially disposed central core composed of metallic tubing of non-magnetic material such as aluminum, for example, a plurality of magnetic core elements each comprising a number of C-shaped laminations made of silicon steel, for example. The (Z-shaped core elements are radially mounted around the core with the ends of the C facing outwardly. A coil of magnet wire is disposed around the core and core elements between the ends of the core elements. The heater may comprise a plurality of arrays of coils and magnetic core elements disposed along the central core. The heater may be provided with housing to protect it from physical harm while in the well bore. Cable leads for energization of the heater extend from the housing for coupling to power means.

The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing, inwhich FIG. 1 is a side elevation-ail view, partly in section, of a down-hole casing heater in accordance with this invention, and

FIG. 2 is a sectional View taken along the line 22 of FIG. 1.

Referring to the drawings, there is shown a tubing heater, indicated generally by the number 10, comprising a core '12, threaded at each end, which has a pair of arrays of 'C-sh-aped magnetic core members 18 disposed between non-magnetic end supports 16 which are bonded to the core 12 as by fillets 14. Each array of laminated core members '18 has 4 members disposed radially at approximately 90 intervals around the periphery of the core 12, although a greater or lesser number of core members 18 could be used. The members 18 are held in position by means of a plurality of bolts 20 which threadedly engage the core 12.

Each of the arrays of laminated core members 18 has a coil 22, 22a of magnet wire disposed around the core and members 18 between the legs thereof. The number of turns and size of wire used is dependent on good transformer design practice and the energization capabilities available down the well bore.

Pairs of leads 24, 26 for energizing the coils 22, 22a are 3,097,282 Patented July 9, 1963 provided. As shown, coil 22 is illustrated as being connected in series with coil 22a, but parallel connections of the two coils may also be made. The coil assembly is, in practice, usually potted in a suitable potting compound (not shown).

In operation the core 12 is coupled to a line or string of tubing and lowered into the well bore near to the location along the casing where heating is needed. The transformer core windings 22, 22a are then energized by any suitable means, usually a down-hole cable connected to an alternating current source located at or near to the well head.

.The casing adjacent to the heater tool 10 constitutes a single turn shorted secondary winding of the casing heating transformer (windings 22, 22a being the primary winding). For best results the maximum diameter of the tool 10, measured across the ends of the magnetic return members 18, should be such that the tool fits closely but freely slidably within the casing. Such an arrangement reduces air gap losses in the magnetic return path of the tool. The casing is therefore heated by the large amount of current flowing through it as the primary winding or windings are energized. Because of the magnetic return provided by the laminations of the core members, the casing (not shown) is heated by induction to a greater extent when the coils 22, 22a are energized than occurs when electrically energized prior art heaters of corresponding size are used.

While the leads 24 are diagrammatically shown as passing along the outside of the core 12, they are, in practice, coupled to suit-able fluid-tight terminal means (not shown).

The invention has been illustrated as comprising a heater having two primary coils 22, 22a. A single coil or more than two coils may be used, however, depending on convenience of manufacturing or the amount of energization of the heater which is intended.

While the present invention has been described in connection with the heating of down-hole casing strings, the heater of the invention is applicable for use in other applications where a section of hollow tubes is to be heated.

Although the magnetic return elements 14 are customarily equally spaced around the core section 12, non-symmetrical spacing may sometimes be used, but with some loss in efficiency of the device.

What is claimed is:

1. A casing heater adapted to be lowered on a tubing string into a string of Well casing comprising an elongated body section made of non-magnetic metal material, said body section having means at each end for rigidly coupling said heater to said tubing string in end to end relationship therewith, at least one array of generally C-shaped magnetic return elements each having a pair of open end ends, said magnetic return elements being symmetrically disposed around said tubular section with their open ends facing outwardly and with their sides being disposed contiguous to said core section, and an electrical primary coil winding being disposed around said core and said magnetic return elements between their ends, said array being disposed between axially aligned non-magnetic metal supporting structures at each end, said supporting structure being frusto-conical in configuration and axially aligned with respect to the heater, the diameter of the supporting structure which is closest to said array being at least as great as the maximum diameter of said array.

2. A casing heater in accordance with claim 1, wherein said magnetic return elements each comprise a plurality of laminations.

3. A casing heater in accordance with claim 1, wherein said heater has a plurality of primary coils disposed in side by side relationship along said core section and each primary coil has an array of magnetic return elements disposed around the coil.

4. A casing heater adapted to be lowered on a tubing 3 string into a string of well casing, comprising an elongated body section having means for rigidly coupling said heater to said tubing, end parts and flattened sides between said end parts, said end parts being Efrusto-conical in configuration with their bases facing each other, said flattened sides being of uniformly dimensioned square transverse cross sectional configuration, at least one array of four magnetic members having integral base and leg elements, each of said members having its base abutting against a side of said body section with the leg elements pointed away from said body, the diameter of said end parts of the body section being at least as great as the diameter across any pair of said magnetic members, the members of said array being similarly disposed with respect to the length of the body, a mult-i-turn electrical primary coil being disposed around said body and the base of said magnetic members between the legs of said magnetic members, and means whereby said coil may be energized, the maximum dimension between the ends of corresponding legs of opposed magnetic members being slightly less than the inner diameter of the easing into which said heater is adapted to be lowered.

5. A casing heater in accordance with claim 4, wherein said body is composed of non-magnetic material.

6. A casing heater in accordance 'with claim 4, wherein said magnetic elements are secured to said body;

7. A casing heater in accordance with claim 4, wherein a plurality of arrays of magnetic members each having a primary coil wound around the base and between the legs are disposed along said body.

References Cited in the file of this patent UNITED STATES PATENTS 2,472,445 Sprong June 7, 1949 2,513,242 inrna-n June 27, 1950 2,810,053 Messner Oct. 15, 1957 

1. A CASING HEATER ADAPTED TO BE LOWERED ON A TUBING STRING INTO A STRING OF WELL CASING COMPRISING AN ELONGATED BODY SECTION MADE OF NON-MAGNETIC METAL MATERIAL, SAID BODY SECTION HAVING MEANS AT EACH END FOR RIGIDLY COUPLING SAID HEATER TO SAID TUBING STRING IN END TO END RELATIONSHIP THEREWITH, AT LEAST ONE ARRAY OF GENERALLY C-SHAPED MAGNETIC RETURN ELEMENTS EACH HAVING A PAIR OF OPEN END ENDS, SAID MAGNETIC RETURN ELEMENTS BEING SYMMETRICALLY DISPOSED AROUND SAID TUBULAR SECTION WITH THEIR OPEN ENDS FACING OUTWARDLY AND WITH THEIR SIDES BEING DISPOSED CONTIGUOUS TO SAID CORE SECTION, AND AN ELECTRICAL PRIMARY COIL WINDING BEING DISPOSED AROUND SAID CORE AND SAID MAGNETIC RETURN ELEMENTS BETWEEN THEIR ENDS, SAID ARRAY BEING DISPOSED BETWEEN AXIALLY ALIGNED NON-MAGNETIC METAL SUPPORTING STRUCTURES AT EACH END, SAID SUPPORTING STRUCTURE BEING FRUSTO-CONICAL IN CONFIGURATION AND AXIALLY ALIGNED WITH RESPECT TO THE HEATER, THE DIAMETER OF THE SUPPORTING STRUCTURE WHICH IS CLOSEST TO SAID ARRAY BEING AT LEAST AS GREAT AS THE MAXIMUM DIAMETER OF SAID ARRAY. 